In many cases it is desirable to locate underground voids, tunnels, pipes or even a sizable volume having a different density than the surrounding material without digging up the ground to determine if such an entity exists and pin-point its location.
The technology available today allows reliable detection of large voids underground using high power pulse signals with time of travel based analysis, and the detection of smaller voids typically close to the surface using seismic waves or ground penetrating radar. Typically the available technology is capable of penetrating up to 10 meters in depth for the detection of small voids (typically of 1-5 meters in diameter) depending on ground conditions such as water content, type of ground composition etc.
However with the current available technologies, it is not possible to reliably detect and locate small voids or tunnels deep underground. Typically, smuggling tunnels, tunnels for infiltration under fences and the like are dug 10-80 meters underground enabling these tunnels to be undetected with the current available technologies. These tunnels typically of 1-5 meters in diameter pose a serious threat as they can be used for illegal actions such as smuggling and carrying out terror attacks.
Also in the field of archeology and geology in many case it is desirable to be able to locate the exact location of sub-surface artifacts and/or abnormalities without performing random digging.